This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Digital broadband broadcast networks enable end users to receive digital content including video, audio, data, etc. Using a mobile terminal, a user may receive digital content over a wireless digital broadcast network.
The capacity of a wireless transmission channel, in a broadcasting system, for example, can be divided between different services by using time-division multiplexing (TDM). Each service reserves a slot in a TDM frame, which results in a fixed bit rate. FIG. 1 illustrates time-frequency (TF) slicing in which each TF frame 100 and 110 is divided into four portions, one for each RF channel (identified as RF1, RF2, RF3, and RF4). That is, the capacity of a fixed TDM frame can be dynamically divided between physical channels for data transmission. Physical channels are TDM channels that reserve the specified slot from the frame, with one physical channel being capable of carrying one or more logical channels. There must be a time shift between the slots of a certain physical channel in different RF channels. This makes it possible to use receivers with one tuner, because the receiver then has time to tune to the new frequency before receiving the next slot. The number of RF channels can be NRF=2, 3, 4, 5, 6 or more in various embodiments. It should be noted that the RF channels used do not need to be adjacent to each other.
Using such time-frequency (TF) slicing, bit rate variations are averaged over all of the services being provided, thereby resulting in a decreased overall bit rate variation and a lower amount of wasted capacity. With TF slicing according to conventional systems and methods, several RF channels are used to increase the size of the TDM frame at issue and to multiplex services over all of the channels. The number of services being provided is increased proportionally relative to the number of RF channels, resulting in an increased statistical multiplexing gain. This arrangement also provides frequency diversity by extending the channel coding and interleaving over all of the available RF channels.
A problem arises when guaranteeing time for tuning to another RF channel between two TF frames in TF slicing is desired in conjunction with a requirement that reception with a single hopping-tuner should be enabled. The problem of slot allocation in the TF scheduler, while requiring a tuning time between TF frames, is discussed below with regard to a previously proposed scheduling concept for TF-slicing. All services slot sizes of Xi/NRF are allocated on each RF frequency in the TF frame. Xi can refer to the amount of orthogonal frequency division multiplexing (OFDM) cells required to carry the data of service i in the current TF frame, and NRF can refer to the number of RF frequencies.
Slots can be shifted, where the shift is the time frequency frame length (TF) divided by the number (NRF) of allocated RF channels, or:
  shift  =                    T        F                    N        RF              .  In other words, the slots are shifted in relation to each other and the upper limit for Xi/NRF is max_slot_length=shift−Ttuning. TF describes the length of the TF frame in OFDM symbols, and Ttuning is the time it takes for the receiver to change to another RF channel. A slot can be divided on one RF as illustrated with respect to RF3 in TF frame 100 and RF4 in TF frame 110 in FIG. 1, where NRF=4.
However, this type of scheduling is not sufficient to guarantee reception with one tuner in situations where no constraints are set for the service bit rates. For example, the scheduling may lead to slot allocations, where sufficient tuning time before or after reception of pilot symbol signaling does not exist. It should be noted in relation to FIG. 1 that pilot symbols P1 and P2 (P1 & P2), which precede every TF frame are described in U.S. patent application Ser. No. 11/686,636, entitled “DVB-H2 SERVICE DISCOVERY FREQUENCY DOMAIN CORRELATION to Auranen et al.
It should be noted that the conventional rules for slot allocation for one tuner reception can be summarized as follows: If the last slot of the current TF frame and the first slot of the next TF frame are on different RF channels, and there is not enough time for tuning before the P1 & P2 signaling, time for tuning shall be reserved after the P1 & P2 signaling. Furthermore, if a slot is divided on one RF in the current TF frame, a slot carrying the same service cannot be divided on another RF in the next TF frame. If the allocation is illegal, the scheduler would, for example, have to perform for some manner of switching of service slots. Because almost every service allocation in conventional TF frame sets some restrictions on allocations in the next TF frame, the slot allocation scheduling becomes a very complex process, where the transmitter needs to perform receiver tests for all services and groups of services or PLPs (Physical Layer Pipes).
Another problem arises in cases where the “common service part” (e.g., teletext) needs to be received in parallel with audio and video services. Conventionally, this cannot be guaranteed in an optimized manner.
In the context of Digital Video Broadcasting-Terrestrial systems (DVB-T), no solution for the above-described issues has been proposed, although the utilization of spare capacity for the purposes of low bit rate services has been considered in U.S. patent application Ser. No. 11/686,661, entitled “DVB-T2H2 Low Bit Rate service” to Henriksson et al. Other related systems and methods are described in U.S. patent application Ser. No. 11/686,628, entitled “Common rate matching slot for variable bit rate services” Vesma et al., and U.S. patent application Ser. No. 11/748,889, entitled “Using BitTorrent Protocol for Best-effort services in DVB-T2M” to Väre et al.